The installation of electrical devices, such as circuit breakers, in switchboard and panelboard apparatus is generally of two types. In one type of installation, circuit breakers are essentially stationarily mounted to structural members or frame of the switchboard, typically with terminal electrical connection effected via bolted joints. Alternatively, circuit breakers may be physically supported solely by the switchboard buswork via these bolted terminal joints. In such stationary installations, inspection and maintenance of the circuit breaker is difficult and quite hazardous if attempted while the switchboard is live. In some situations, the hazards must be assumed, since de-energization of the switchboard and thus interruption of electrical service to all of the branch circuits in the switchboard cannot be tolerated. To reduce the hazards of working with live switchboards, devices are provided with plug-in or stab-type primary disconnect contacts which do not require direct contact and manipulation to effect their connection and disconnection with mating disconnect contacts of the switchboard. Thus, the device, e.g. circuit breaker, can be plugged in and unplugged from a live switchboard in relative safety.
In higher current applications, the circuit breakers are physically large and quite heavy, thus rendering the bodily movement of the circuit breaker necessary to electrically connect and disconnect it from the switchboard cumbersome if not impossible, unless mechanical assistance is afforded. Not only does the weight and bulk of the circuit breaker become difficult for the electrician to handle, but, as the current ratings increase, the contact pressures of the primary disconnect contacts become extremely difficult, if not impossible to overcome. To surmount these problems, so-called "drawout" apparatus has been resorted to for both supporting the circuit breaker and affording mechanical assistance in overcoming the extreme contact pressures of the disconnect contacts.
Drawout apparatus are typically designed to support the electrical device for racking movement between an extended position well out of an enclosure compartment and an engaged position within the compartment where the load current carrying primary disconnect contacts of the device and enclosure are fully engaged. Since electrical devices, such as circuit breakers for industrial applications, are typically equipped with a variety of accessorial functions served by external auxiliary circuits, provisions must be made for making and breaking these auxiliary circuits as the circuit breaker is moved between its extended and engaged positions. To this end, so-called mating secondary disconnect contacts are mounted with the circuit breaker and the enclosure. These secondary contacts are engaged while the circuit breaker is in the engaged position and become disengaged at some point during movement of the breaker out to the disengaged position. It is common practice to provide a test position for the circuit breaker intermediate its engaged and extended positions where the primary contacts are separated but the secondary contacts are still engaged. In this test position, the accessorial functions can be thoroughly tested in safety while the breaker is "dead."
The secondary contacts carried with the circuit breaker and the secondary contacts mounted by the enclosure begin engaging as the carriage approaches the test position, just as the circuit breaker-enclosure primary contacts begin engaging as the carriage approaches the engaged position. As a consequence, the two sets of secondary contacts must be rather precisely mounted such that they are aligned for smooth, sliding interengagement incident to movement of the carriage into the test position from the extended position.
It is accordingly an object of the present invention to provide drawout apparatus having improved secondary contact mounting provisions effective to provide the requisite alignment of the device and enclosure secondary contacts for positive electrical contacting engagement therebetween.
Another object of the invention is to provide drawout apparatus of the above character wherein the requisite secondary contact alignment is achieved automatically and incident to racking movement of the device into the enclosure.
A further object is to provide drawout apparatus of the above character wherein a large plurality of device and enclosure secondary contacts are accommodated.
Yet another object of the present invention is to provide drawout apparatus of the above character which is reliable in operation, efficient in design, and inexpensive to manufacture.
Other objects of the invention will in part be obvious and in part appear hereinafter.